1. Field of the Invention
The present invention relates generally to an ink-jet printing method and an apparatus therefor, which can obtain high quality printed image on a printing medium, and more particularly to an ink-jet printing method and an apparatus therefor, in which a printing ink and a printing property improving liquid coagulating a coloring agent of the printing ink or making the coloring agent insoluble, are ejected on a printing medium.
The present invention is applicable for all of devices or apparatus employing paper, cloth, non-woven fabric, OHP sheet, and so forth, and even a metal as a printing medium. In concrete, the present invention is applicable for office appliance, such as printer, a copy machine, facsimile and so forth, industrial production machines or so forth.
2. Description of the Related Art
Ink-jet printing systems have advantages of low noise, low running cost, easiness of down-sizing and providing color printing capability for the apparatus, and so forth, and have been widely used in printers, copy machines and so forth.
However, when an image is printed on a printing medium, such as a plain paper and so forth, it is possible that water resistance of the printed image is insufficient. Also, in case of printing of color image, it is somewhat difficult to achieve both of high density image which may not cause feathering and an image which may not cause bleeding between adjacent colors. Therefore, it is often impossible to obtain high quality color image with high image fastness.
As a method to improve water resistance of the image, an ink containing color agent which is provided water resistive property, has been put into practical use. However, water resistance of the image is still insufficient in many case. In principle, the ink containing water resistive coloring agent is an ink which is difficult to solve in the water after once dried. Therefore, such ink can easily cause plugging of ink-ejection openings in an ink-jet head. Also, a construction of the apparatus for preventing plugging of ink can be complicated.
On the other hand, in the prior art, there are large number of technologies for improving fastness of the medium to be printed. For example, in Japanese Patent Application Laid-open No. 24486/1978, there is disclosed a technology for fixing by laking dye through post-treatment of the dye product.
Japanese Patent Application Laid-open No. 43733/1979 discloses a method for perform printing employing two or more components which may enhance film forming performance by mutually contacting at normal temperature or upon heating, utilizing an ink-jet printing system. By this, mutually contacting respective components on the printing medium may form a printing product with a film firmly fixed on the printing medium.
Also, in Japanese Patent Application Laid-open No. 150396/1980, a method for applying water-resistance agent forming a lake with a dye after printing with a water soluble ink by ink-jet system, is disclosed.
In Japanese Patent Application Laid-open No. 128862/1983, an ink-jet printing method for printing a printing ink and printing property improving liquid in overlapping manner with preliminarily identifying position of the image to be printed. In the disclosed method, the image is printed with the printing property improving liquid in advance of printing by the printing ink, the printing property improving liquid is applied in an overlapping manner on the printing ink printed in advance, the ink is applied an overlapping manner on the printing property improving liquid in advance, and then the printing property improving liquid is applied over the printing ink in an overlapping manner.
It has been known that separately applying the printing ink and a printing property improving liquid is effective for improving light-resistance, water-resistance, image density and chroma.
However, the above-mentioned publications are silent about a recovery means for maintaining reliability of ejection, which is specific to an ink-jet printing apparatus, a head construction, a tank construction, a printing mode for enhancing quality of the printed image and so forth.
Application of the printing ink and the printing property improving liquid as disclosed in Japanese Patent Application Laid-open No. 128862/1983 may cause a different nature of respective printing pixels at a different order of ejection.
Spreading of the printing ink and the printing property improving liquid are diagrammatically illustrated in FIGS. 1A and 1B. FIG. 1A shows the case where the printing property improving liquid is ejected in advance of the printing ink. In this case, the coloring agent in the printing ink, such as dye and so forth stays relatively close to the surface in the depth direction to enhance color development ability of the printing ink. The dot shape is considered to form a circular dot with less feathering. On the other hand, when the printing ink hits on the printing medium, in conjunction therewith reaction with the printing property improving liquid to cause coagulation is started. Therefore, the component of the coloring agent in the printing ink may not penetrate into the printing medium and thus tends to make the dot side smaller.
FIG. 1B shows the case where the printing property improving liquid is ejected on the printing ink which is ejected in advance, in contrast to the case of FIG. 1A. When the printing ink is ejected in advance, higher water-resistance can be attained in comparison with the case where the printing property improving liquid is not applied. However, since the printing ink penetrates into the inside of the depth direction of the printing medium, the color development ability of the printing ink cannot be improved.
Furthermore, if the order of ejection of the printing ink and the printing property improving liquid is different, hue can become different in either case. It is considered that, even with the equal amount of printing ink, distances between the coloring agent component, such as dye and so forth are differentiated depending upon the manner of coagulation of the ink to cause difference of hue.
As set forth above, depending upon the order of ejection of the printing ink and the printing property improving liquid, the image to be formed can be differentiated.
Also, color development, hue, dot configuration may be differentiated depending upon the position in the depth direction of the printing medium where mixing of the printing ink and the printing property improving liquid is caused. Such condition is caused when time intervals from hitting of the printing property improving liquid on the printing medium to hitting of the printing ink are differentiated between the pixels. This also influences the formed image, significantly.
The followings are discussion for influence of these natures for the image in the conventional ink-jet printing system.
1) When printing is performed by a printing method to form an image with the printing property improving liquid in advance of that of the printing ink as disclosed in Japanese Patent Application Laid-open No. 128862/1983, or a printing method to print the image with the printing ink overlapping with the image printed with the printing property improving liquid, and again print the printing property improving liquid on the image of the printing ink, the dot diameter can become smaller than that not employing the printing property improving liquid. When two modes of a printing mode employing the printing property improving liquid and a printing mode not employing the printing property improving liquid, under the conventional ejection amount designed adapted not to employ the printing property improving liquid, the image, in which lines becomes visually perceptible, can be formed when printing is performed employing the printing property improving liquid.
2) In case of conventional monochrome printing, such as that with Bk ink and so forth, reciprocal printing has been performed for high speed printing. In the printing where a printing property improving liquid ejecting head and a printing in ejecting ink are simply arranged in alignment in the reciprocating direction, the orders of ejection of the printing ink and the printing property improving liquid are differentiated in the forward direction and reverse direction, band fluctuation (color fluctuation, density fluctuation, line fluctuation) in the width of the head width, which has not be caused conventionally, can be caused.
3) FIGS. 2A, 2B and 2C show the case of ideal head. A reference numeral `denotes a head, 2 denotes an ejection nozzle, 3 denotes an ejected ink droplet. FIG. 2A shows a manner to eject the ink droplet from the head. FIG. 2B shows a behavior of the dot formed on the printing medium. FIG. 2C shows a distribution of ejection density of the ink in the printing medium. In the practical head, due to tolerance information of the nozzle, nozzle distribution (ejection amount distribution, ejecting direction) can be caused. Therefore, density of the printing ink on the printing medium can be differentiated to form the density fluctuation, line on the printed image. Also, similar density difference of the printing property improving liquid on the printing medium can be caused in application of the printing property improving liquid. Thus reaction amount of the printing ink may be differentiated per ink to cause density difference, color difference and line.
4) In a head unit, in which conventional heads for respective colors are combined, it is difficult to precisely match the registration position between respective heads in the positioning method between the heads (different depending upon the head and main body construction) due to tolerance in production and other reason. Therefore, in a range not to influence the image, certain magnitude of offset has been permitted. In case offsetting of the registration between respective heads of the printing property improving liquid and the printing ink, when the order of ejection of the printing ink and the printing property improving liquid and/or ejection interval is differentiated, density fluctuation, color fluctuation or line can be caused on the image.
5) In the printing method to print the printing property improving liquid and the printing ink in overlapping manner as disclosed in Japanese Patent Application Laid-open No. 128862/1983, little improvement of color development and little improvement of feathering of the dot configuration can be observed.